One of the major technological innovations in the last two decades or so has been the development of maintenance-free battery for automotive applications and this technology is now widely used in the battery industry world-wide.
However, since most of the automotive batteries contain free electrolyte, the hazards of acid leaks still persist particularly during battery handling, transportation and charging. Acid spillage or leakages are most undesirable, for they can cause burns, corrosion of battery terminals and the related electrical systems in the automobile. As a result, there is a definite preference in the market place for a safe, leak-proof battery, which can be handled more easily without posing any hazard. In view of this, a small percentage of automotive batteries are being converted to leak-proof, valve regulated type assembled with AGM (Absorptive Glass Mat) separators, especially for the premium range of vehicles.
However, valve regulated automotive batteries are substantially more expensive to manufacture. Furthermore, the flooded battery designs are known to have certain technical advantages in comparison to the acid-starved, VTLA (Valve Regulated Lead Acid) designs. In spite of substantial cost penalties as well as certain technical limitations, the trend appears to be towards valve regulated type due mainly to the need for a safe, leak-proof maintenance-free battery. For example, most of the future designs for a 36V automotive battery are of VRLA type assembled with AGM separators.
It is clear from the above that further technical developments are required to make leak-proof or leak-resistant automotive batteries of flooded variety. These designs are still predominantly used all over the world primarily due to their lower cost as well as the ease of manufacturing.
Hitherto, there have been many attempts to develop a leak-resistant automotive battery with free electrolyte using a specially designed battery cover.
In this context, some of the important innovations, which have taken place in the last 20 years, are being discussed as hereinbelow.
U.S. Pat. No. 4,348,466 published on Sep. 7, 1982 (assigned to Varta Battery Ltd., Willowdale, Calif.) discloses an anti-spill arrangement for a liquid electrolyte battery which comprises a large rectangular chamber with an inlet in communication with a respective battery cell and an outlet in communication with a vent to the atmosphere. The chamber and the associated passages have sufficient volume to retain the electrolyte flows when the battery is tipped or rotated. Furthermore, the chamber arrangement is such that the level of the contained electrolyte remains spaced from the outlet.
When the chamber and the passages are filled with electrolyte, an air lock is developed which prevents additional flow of electrolyte from the cell to the chamber and the passage configuration. The notable point in this patent is that large chambers and passage configuration allow substantial amount of electrolyte to flow into the battery cover and thereby increase the likelihood of electrolyte spilling into the venting area, ultimately causing leakage of the electrolyte from the battery system, especially if the battery is vibrated or agitated. Furthermore, this patent does not provide leak protection in the inverted position of the battery.
German patent No. 4,216,563 published on Nov. 24, 1993 (assigned to VB Autobatterie GmbH) discloses a double-cover type construction having a chamber associated with each cell. Each chamber is properly sized such that when the battery is tilted, only a limited amount of acid from the respective cell enters the collection chamber which the chamber can contains. In the inverted position, however, a substantial amount of electrolyte flows out from the cells into the cover, thus increasing the risk of electrolyte leaking from the battery.
In U.S. Pat. No. 5,380,604 to Hampe et al. (issued on Jan. 10, 1995) and U.S. Pat. No. 5,424,146 to Lin (issued on Jun. 13, 1995), similar configurations have been seen.
The leak-resistant battery cover comprises two parts, i.e. an upper lid and a lower lid, having chamber associated with each cell. Each chamber has guides for controlling the flow of acid. The guides are so designed that in any position of the housing, when resting on one of the side walls, acid within the chambers remains below the critical level, above which acid flows into a spark arrestor.
However, a significant amount of electrolyte is allowed to flow into the respective cover, which increases the possibility of acid leakage when the battery is vibrated or agitated. Also, there is little or no protection against electrolyte leakage when the battery is inverted.
U.S. Pat. No. 5,683,830 issued on Nov. 4, 1997 and U.S. Pat. No. 5,843,593 issued on Dec. 1, 1998 (assigned to Douglas Battery Manufacturing Company, U.S.A) disclose a leak resistant battery cover having two parts. The battery cover provides a labyrinth of passages forming a path from each cell vent to the atmospheric vent. The labyrinth provides a portion of each path above a level which the electrolyte attains when the battery is tilted or rotated 90° from an upright position.
European Patent No. EP 0 639 862 B1 published on Sep. 18, 1996 (assigned to VB Autobatterie GmbH) discloses a multi-cell battery having a central gas venting system integrated with the battery cover and incorporating a gas collecting duct and providing in the side wall of the cover a depression which is connected by a side duct to the collecting duct and an insert is provided in the depression. The insert contains a porous frit closing the gas duct, which is connected to the cover in an air-tight manner. The frit is so arranged in the insert that its lower edge is always above the level of the acid return flow.
The aforementioned Patents are generally based on relatively complex configuration of a battery cover, which comprises two parts, i.e. an upper lid and a lower lid and the upper lid is then sealed with the main cover either ultrasonically or by heat sealing. These designs of battery are relatively expensive and more complex at the manufacturing stage. Clearly, there is a need for a simple, leak resistant cover without having any adverse effect on its cost competitiveness.